Remote sensing vehicles such as satellites are commonly used for electro-optical, infrared, and RF imaging of the surface of celestial bodies, such as the earth. FIG. 1 illustrates one such system known in the prior art for capturing swaths/images of a target surface of a celestial body. As a particular remote sensing vehicle orbits in a certain flight advancement velocity (i.e., illustrated by the V arrow), a sensor is pointed at Nadir (in elevation, or along-track, angle) and perpendicular to the flight direction. In a pushbroom system, the image sensor covers the entire cross-track dimension, whereas in a whisk-broom system, the image sensor is scanned in the cross track direction rapidly as the vehicle is travelling, usually more slowly, in the along-track direction. In a whisk broom scanning satellite, a mirror rapidly scans in the cross-track direction to effectively point the sensor at a target surface for imaging. As the vehicle advances, the sensor captures swaths of the target surface area to generate an image. Such whisk broom scanning is implemented with the Visible Infrared Imaging Radiometer Suite (VIIRS) satellite-mounted sensor. A VIIRS satellite sensor payload is a scanning radiometer that collects visible and infrared imagery and radiometric measurements of land, atmosphere, cryosphere, and oceans. VIIRS data is used to measure cloud and aerosol properties, ocean color, sea and land surface temperature, ice motion and temperature, fires, and Earth's albedo, for instance. Climatologists use VIIRS data to improve our understanding of global climate change.
As illustrated in FIG. 1, when collecting data or scanning at Nadir elevation angle with such a remote sensing vehicle, a particular resulting swath/image is bowtie-shaped (due to the curvature of the celestial body when scanning at Nadir). Due to this bowtie shape, successive swaths 1 and 2 will have a pixel underlap between the middle portion of such swaths 1 and 2, as shown. Overlap is also prevalent at corner areas of the adjacent swaths 1 and 2, as shown. Both the underlap and overlap issues can be problematic when stitching the swaths together to generate a desired image. In particular, underlap results in incomplete coverage of the celestial body, leaving gaps in collected data. There also exists issues with time delay and integration (TDI) dwell when scanning at Nadir with the VIIRS satellite because of the limitations of the sensor platform being static relative to the host bus.
One solution to address these issues is to manually change the pointing angle of the sensor platform during sensor integration to the satellite. However, this solves only the underlap issue, and does not address other issues such as TDI being tied to the gross satellite bus motion. Another solution involves changing the angular position of the Nadir deck while in orbit. Another solution involves changing the attitude of the satellite bus itself while in orbit. Finally, yet another solution involves changing the sensor itself, such as changing the “heartbeat” master clock, scan rate, and/or optical design.
These prior solutions often result in unintended consequences or transient behaviors of the satellite bus, and can make the scan-to-scan (revisit) and instrument-to-instrument comparisons less tractable. This is exacerbated by the fact that the host bus typically has many other sensors on-board, so changing the attitude of the host bus can negatively affect such ancillary sensors.
Reference will now be made to the exemplary embodiments illustrated, and specific language will be used herein to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended.